• Document: CHAPTER 13 LECTURE SLIDES
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CHAPTER 13 LECTURE SLIDES Prepared by Brenda Leady University of Toledo To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please note: once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you advance the next slide. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Gene regulation refers to the ability of cells to control their level of gene expression  Majority of genes regulated so proteins produce at certain times and in specific amounts  Constitutive genes are unregulated and have essentially constant levels of expression 2 Overview  Benefits of gene regulation  Conserves energy – proteins produced only when needed  Ensures genes expressed in appropriate cell type and at the correct stage in development 3 Gene regulation in prokaryotes  Often used to respond to changes in the environment  Escherichia coli and lactose example  When lactose is not present, E. coli does not make a lactose permease (lactoset transporter) and β- galactosidase  When lactose is available, the proteins are made  When lactose levels drop, the proteins are no longer made 4 5 Gene regulation in eukaryotes  Produces different cell types in an organism or cell differentiation  All of the organism’s cells contain the same genome but express different proteomes  Different proteins  Different amounts of the same protein 6 7 Developmental gene regulation in mammals  Fetal human stage characterized by continued refinement of body parts and a large increase in size  Gene regulation determines which globin polypetides are made to become functional hemoglobin  Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin  Allows fetus to harvest oxygen from maternal blood 8 9 Gene regulation can occur at different points  Bacterial gene regulation  Most commonly occurs at the level of transcription  Or control rate mRNA translated  Or regulated at protein or post-translation level 10  Eukaryotic gene regulation  Transcriptional regulation common  RNA processing  Translation  Post-translation 11 Transcriptional regulation in bacteria  Involves regulatory transcription factors  Bind to DNA in the vicinity of a promoter and affect transcription of one or more nearby genes  Repressors inhibit transcription  Negative control  Activators increase the rate of transcription  Positive control 12 13  Transcriptional regulation also involves small effector molecules  Binds to regulatory transcription factor and causes conformational change  Determines whether or not regulatory transcription factor can bind to DNA  2 domains in regulatory transcription factor that respond to small effector molecules  Site where protein binds to DNA  Site for small effector molecule 14 15 Operon  Operon in bacteria is a cluster of genes under transcriptional control of one promoter  Regulatory region called operator  Transcribed into mRNA as polycistronic mRNA – encodes more than one protein  Allows regulation of a group of genes with a common function 16 lac operon  In E. coli contains genes for lactose metabolism  lacP - promoter  3 structural genes  lacZ – β-galactosidase  Allolactose important in lac operon regulation  lacY – lactose permease  lacA – galactosidase transacetylase 17  Near the lac promoter are 2 regulatory sites  lacO – operator – provides binding site for repressor protein  CAP site – activator protein binding site  lacI gene - codes for lac repressor  Considered a regulatory gene since its sole function is to regulate other gene’s expression  Has its own promoter (not part of lac operon) 18 19  When lactose is absent  Lac repressor protein binds to nucleotides of lac operator site preventing RNA polymerase from transcribing lacZ, lacY and lacA  RNA polymerase can bind but not move forward

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